🧵 Everything You Ever Wanted to Know About JavaScript Strings

A language is what we use to talk to machines; strings are what we use to talk to people.”

1 Primitive vs Object Strings

jsCopyEditlet s  = "Hello World";
console.log(typeof s);  // "string"

let s1 = new String("Hello");
console.log(typeof s1); // "object"

Why care? Primitive strings are lightweight and immutable; new String() builds a heavy wrapper. Use primitives 99 % of the time.

---

2 Immutability in Action

jsCopyEdits[0] = "p";      // 🚫 does nothing
console.log(s);  // "Hello World"

Strings can’t be mutated in place—you always get a new string.

---

3 Bread‑and‑Butter Methods

---

4 Strict vs Loose Comparison

jsCopyEditlet str1 = "Hello";
let str2 = "hello";

str1 === str2; // false
str1 ==  str2; // false

Use ===—avoid coercion surprises.

---

5 Escaping Quotes

jsCopyEditlet quote = "He said, \"Hello, World!\"";
console.log(quote);

---

6 A Dash of Regex

jsCopyEdit/World/i.test("Hello, World!"); // true

Regex + strings = super‑powers: validation, search‑and‑replace, parsing.

---

7 Full Code Playground

let s = "Hello World";
console.log(typeof s);               // "string"

let s1 = new String("Hello");
console.log(typeof s1);              // "object"

// Immutability
s[0] = "p";
console.log(s);                      // "Hello World"

// Core 
console.log(s.length);               // 11
console.log(s[0]);                   // "H"

console.log(s.indexOf("l"));         // 2
console.log(s.lastIndexOf("l"));     // 9
console.log(s.slice(1, 4));          // "ell"
console.log(s.substring(1, 4));      // "ell"
console.log(s.substr(1, 4));         // "ello"
console.log(s.replace("l", "p"));    // "Heplo World"
console.log(s.toUpperCase());        // "HELLO WORLD"
console.log(s.toLowerCase());        // "hello world"
console.log(s.charAt(0));            // "H"
console.log(s.charCodeAt(0));        // 72
console.log(s.split(" "));           // ["Hello", "World"]
console.log(s.includes("l"));        // true
console.log(s.startsWith("Hello"));  // true
console.log(s.endsWith("World"));    // true
console.log(s.repeat(3));            // "Hello WorldHello WorldHello World"
console.log(s.trim());               // "Hello World"

// Comparisons
let str1 = "Hello";
let str2 = "hello";
console.log(str1 === str2); // false
console.log(str1 ==  str2); // false

// Escaping
let quote = "He said, \"Hello, World!\"";
console.log(quote); // "He said, \"Hello, World!\""


// Regex
let regex = /world/i;
console.log(regex.test("Hello, World!")); // true

---

8 Takeaways

1. Prefer primitives; wrappers add weight.

2. Strings are immutable: every method returns a brand‑new string.

3. Master search, extract, replace, and regex for real‑world tasks.